This invention relates to equipment used in electronic media reading and writing, and more particularly to systems using data recording tape.
Tape read/write head assemblies include one or more read/write transducer heads positioned transverse to the intended path of a recording tape. The transducer heads write data on and read data from parallel tracks on the tape called xe2x80x9cdata tracks.xe2x80x9d The head assembly can move laterally across the width of the tape to position a particular transducer head relative to a particular data track, with the head assembly""s position controlled by a servo.
The tape itself may include tracks called xe2x80x9cservo tracks,xe2x80x9d which provide information to control the lateral position of the head assembly. Servo tracks serve as reference features or guide marks on the tape. By monitoring the position of the head assembly relative to the servo tracks, the head assembly can dynamically adjust the position of the transducer heads to keep the heads in a correct position relative to the tape tracks. Ideally, the tape path past the head assembly should not vary, but in practice lateral tape movement affects the position of a transducer head relative to a track. Dynamic repositioning is important because it compensates for the lateral movement.
In part because of servo control, data track widths have been made significantly narrower and the capacity of the recording medium has been increased. With a decrease of the width of data tracks and an increase of the number of tracks on a width of tape, servo control takes on added significance and greater precision is advantageous. The position of the transducer heads of the head assembly relative to tape tracks can become sensitive to a variety of disturbances, some of them minute.
Disturbances may arise, for example, from the equipment used to dispense the tape that is being fed past the transducer heads and from the equipment used to take up the tape after it had passed the transducer heads. In a typical case, for example, tape is dispensed from a first reel, which includes a hub and which often includes a flange, and is taken up by second reel. If a hub or a spindle supporting a reel is not perpendicular to the reel, the reel may wobble as it rotates. This wobble causes the tape to move laterally relative to the head assembly.
In addition, contact between the tape edge and the flange may produce lateral movement of the tape. When tape is taken up on a reel at high speed, for example, small pockets of air may become trapped between layers of tape, allowing one layer to slip laterally relative to another. Another potential source of lateral tape motion may come about due to the interaction between the head assembly and the tape. At times when the head assembly moves laterally relative to the tape to find a particular track, friction between the head assembly and the tape causes the tape to adhere to the head assembly and xe2x80x9cfollowxe2x80x9d the head assembly.
Some of the lateral movements described above involve rapid changes in the lateral position of the tape relative to the head assembly, and other movements involve gradual changes. In the case where the tape follows the moving head assembly, for example, the initial tape movement may be gradual. There may come a point, however, at which the tension in the tape overcomes the frictional force, and the tape rapidly snaps back to a previous position.
The invention provides systems that sense the lateral movement of data recording tape such as magnetic recording tape. One system monitors the tape position and adjusts the tape path based upon the tape position. Another system monitors the tape position and adjusts the position of the head assembly. The systems will be described separately, but typically the systems cooperate with each other to compensate for rapid (or xe2x80x9chigh-frequencyxe2x80x9d) changes and for more gradual (or xe2x80x9clow-frequencyxe2x80x9d) changes in tape position.
In one embodiment, the present invention provides a system for positioning data recording tape. The system includes a sensor that detects the position of the tape and issues a position signal as a function of the tape position. The sensor may be, for example, an optical sensor or a magnetic sensor, and the signal may indicate how close the tape is to a target tape path. The system also includes a guide that interacts with the tape and a controller that moves the guide as a function of the position signal. By moving, the guide steers the tape. One technique for steering the tape with the guide is by tilting the guide.
In another embodiment, the present invention presents a system for positioning a head for reading and writing to data recording tape. The system includes a head, a sensor configured to detect the position of the tape and generate a signal as a function of the position, and a servo coupled to the head. The servo is configured to move the head as a function of the signal. Typically the sensor is located such that the sensor detects the tape""s position before the tape passes the head. The system may also include an adaptive estimator, which receives the signal. Based upon the detected position or movement of the tape, the adaptive estimator may generate a second signal, which is used by the servo to move the head. With this system, the servo may move the head in anticipation of a disturbance that has not yet reached the head.
In a further embodiment, the present invention provides a method for steering data recording tape. The method includes passing the tape over a guide, sensing the position of the tape, generating a signal as a function of the position, and moving the guide as a function of the signal.
In still another embodiment, the present invention provides a method for moving the head in anticipation of tape disturbances. The method comprises detecting a disturbance in the path of the tape before the disturbance reaches the head, generating a signal as a function of the disturbance, and moving the head as a function of the signal.
In an additional embodiment, the present invention presents a system that includes a sensor that detects the position of data recording tape and issues a position signal as a function of the position of the tape. The system also includes a guide that interacts with the tape, a first controller that moves the guide as a function of the position signal, a head and a second controller that moves the head as a function of the position signal. The controllers may send signals to each other.
In a further embodiment, the present invention presents a control method. The method includes passing data recording tape over a guide and past a head. The position of the tape is sensed, and a position signal is generated as a function of the position of the tape. The method further includes moving the guide as a function of the position signal and moving the head as a function of the position signal.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.